1. Field of the Invention
The invention relates to a method of constructing a rail track and in particular to a method of constructing a rail track on a concrete slab in which the concrete slab is poured around anchor members for fixing tie plates supporting the rails of the rail track. The invention also relates to a temporary tie plate used in the method according to the invention.
2. Description of the Prior Art
Laying a rail track for metros or trams on a concrete slab by placing prefabricated rails directly onto tie plates at the location where the track is to be laid, the rails being suspended in their final position by means of a gantry with the tie plates fixed to the rails by attachments, is currently known in the art. A concrete slab is then poured under the rails, up to the height of the tie plates, which support anchor members consisting of threaded rods passing through the tie plates and having a bottom part embedded in the concrete slab. When the concrete has set, the tie plates are permanently immobilized on the concrete slab by tightening nuts onto the threaded rods, the nuts bearing on the top face of the tie plates.
The above kind of method of constructing a rail track nevertheless has the disadvantage of being subject to problems with the formation of air bubbles under the tie plates when pouring the concrete, which prevents the formation of a properly flat concrete bearing surface under the tie plates. Accordingly, when the nuts are tightened onto the threaded rods to immobilize the tie plates after the concrete has set, it is common for the tie plate to move because of the imperfect bearing surface. It is then necessary to demount the tie plate and make good the bearing surface manually to enable correct positioning of the tie plate. This reworking of defective bearing surfaces is time-consuming and costly and considerably slows down laying the rail track.
Also, one object of the present invention is to propose a simple and economic method of producing a rail track that forms without major defects bearing surfaces on which the tie plates supporting the rails rest.
To this end, the invention provides a method of constructing a rail track on a concrete slab, in which method said concrete slab is poured around anchor members for fixing tie plates supporting rails of the rail track, which method includes the following steps:
suspending temporary tie plates at the location where the tie plates supporting the rail track are to be placed, the temporary tie plates supporting anchor members adapted to be partly embedded in the concrete and including vents for evacuating air trapped under the bottom face of the temporary tie plate when pouring the concrete slab,
pouring a concrete slab up to the height of the temporary tie plates,
removing the temporary tie plates after the concrete slab has set, and
placing the tie plates supporting the rails accurately in their final position and fixing the tie plates to the anchor members.
According to another feature of the invention the rails are suspended above the location where the concrete slab is to be poured by means of a gantry, the rails having permanent tie plates premounted on them, the temporary tie plates being placed under the tie plates and then moved into the required position by means of the gantry.
According to a further feature of the invention, after the step of removing the temporary tie plates and before the step of placing the permanent tie plates, any flashing formed on the surface of the concrete slab by concrete rising up through the vents is scraped off.
The invention also provides a temporary tie plate for use in the method according of constructing a rail track previously described, which temporary tie plate includes a body whose bottom face, with which the concrete comes into contact when pouring the concrete slab, includes vents.
In particular embodiments the temporary tie plate according to the invention can have any of the following features alone or any technically feasible combination:
the body of the temporary tie plate comprises a plate with multiple through-holes;
the periphery of the plate includes a step having a top edge inclined relative to the plane of the bottom face of the plate to provide a reference when forming the concrete surface of the track slab when the latter must incorporate a slope for drainage;
the body of the temporary tie plate includes openings with a larger diameter than the vents to enable anchor means to pass through them.
Objects, aspects and advantages of the present invention will be understood better from the description of one particular and non-limiting embodiment of the invention given hereinafter and with reference to the accompanying drawings.